Structure of adsorbed and grafted single-stranded DNA fragments on aminated latex particles: A small-angle neutron scattering study

Adsorption and covalent binding of polythymidylic acid (dT(35)) On aminated polystyrene latex particles have been studied. Both the electrostatic inte ractions between negative charges of the dT35 and the positive charges of t he cationic latex particles and hydrophobic interactions are the driving fo rces for the adsorption. Small-angle neutron scattering (SANS) has been use d to determine the structure of the adsorbed or grafted dT(35) layers. The thickness of the adsorbed oligonucleotide layer on the latex particles is s mall with respect to the extended length of dT(35) molecules (similar to 12 0 Angstrom) indicating that the adsorbed molecules lay close in a flat conf ormation on the surface, irrespective of the pH and ionic strength. In cont rast, the covalently grafted dT(35) molecules at basic pH and high surface coverage extends more radially into the solvent, giving rise to a thicker l ayer in comparison to the case of adsorption.